Field of the Invention
The present invention relates to a power supply device that suppresses an influence on on-vehicle electrical equipment caused by an operation of an electric supercharger that is arranged in an intake air passage of an internal combustion engine and is driven by an electric motor. In particular, the present invention relates to a power supply device for a vehicle which uses two power supplies such as a battery and a capacitor that can be charged and discharged in a short time compared to the battery.
Background Art
In recent years, engine downsizing with supercharger technology is widely used as one of fuel economy improvement measures of an internal combustion engine. The engine downsizing with supercharger technology supercharges the internal combustion engine by means of a supercharger to increase a power output and reduce an engine displacement while the same power output is maintained. The downsizing of the engine displacement can reduce pumping loss or mechanical losses to improve fuel economy. There has been developed an electric supercharger to which an electric motor is attached to improve transient responsiveness of the supercharger and to compensate for an insufficient supercharging of the supercharger at low engine speeds.
When the electric supercharger is driven, a large current necessary for a large power output flows to the electric supercharger. For this reason, there is a possibility that voltage drop or voltage fluctuation occurs across battery terminals to adversely affect other on-vehicle electrical equipment.
For example, Patent Document 1 proposes a technology in which, when the power output of the electric supercharger is equal to or greater than a threshold value, a power supply system for the electric supercharger and a generator are disconnected from other on-vehicle electrical equipment or the battery, the electric supercharger is driven by power generation of the generator, and other electrical equipment are driven by a battery power. In this way, voltage fluctuation in the battery caused by a large electrical power consumption of the electric supercharger is suppressed from adversely affecting other electrical equipment.
In addition, for example, in Patent Document 2, the battery and a capacitor are used as power supplies for the electric supercharger, the capacitor with good charging and discharging characteristics is used to drive the electric supercharger at an initial drive phase, and thereafter, the battery and the capacitor are connected in parallel to each other to drive the electric supercharger.    [Patent Document 1] JP-A-2003-161157    [Patent Document 2] JP-A-6-346747
However, in Patent Document 1, when the electric supercharger is driven, the generator supplies electrical power to the electric supercharger, but, there is a possibility that, since the generator is driven by engine power, the power output of the engine is reduced not to deliver an acceleration which a driver demands. In addition, when power generation of the generator is increased, an engine load is increased and fuel economy is worsened.
In addition, in Patent Document 2, since the capacitor has characteristics that a voltage of the capacitor is decreased depending on SOC, the battery and the capacitor are connected in parallel to each other, and the capacitor takes most electrical power from the battery to drive the electric supercharger while the SOC remains as it is. When large electrical power is frequently input to and output from the battery, the battery is deteriorated.